See if the rubbery water seal eases off, if so put it back again
with some clear silicone sealant, the cheap stuff that comes in cartridges
for cartridge guns will do. Water soaking into the carpets is not good
as there isn't enough air circulation to dry it out, rust soon takes a hold.
Common ways of tracing water ingress are sheets of newspaper, see
where they get wet first, or remove carpet and sprinkle talcum powder.

In passing Fiat (and other makes) doors rust along bottom due to the
seal shrinking or being short as installed, at speed water is driven back
along the glass, then sprays into the door interior around the lock area.
The drain holes in the bottom of the door don't have much paint, and
water also wicks into the folded seam.